Environmental factors are known to have far-reaching effects on nervous system functioning and play a crucial role in the etiology of many human disease processes. This project investigates whether social stimulation can influence neuroplasticity in the adult brain through the proliferation, survival, and regeneration of new cells (neurons or glial cells). The methodology will include the use of acoustic stimulus presentations, endocrinological manipulations, lesioning studies, and molecular biology techniques (e.g., immunohistochemistry, and in situ hybridization) to test hypotheses concerning the modulation of neuroplasticity by social stimulation. Specific Aim 1 investigates whether social experience modulates cell numbers in the brain via changing cell proliferation or survival, and examines the role of brain-derived neurotrophic factor in such modulation. Specific Aim 2 tests the hypothesis that alterations in sex steroid levels, particularly androgens, in response to social cues are a mediating factor inducing changes in cell proliferation and/or survival. Specific Aim 3 bears the most direct relevance to human health and examines the hypothesis that social modulation facilitates neuronal regeneration after brain injury. This project will increase our understanding of how social interactions, with or without concomitant hormonal changes, affect cell proliferation and survival in brain regions mediating sexual behavior and endocrine regulation. In addition, these studies will also shed light on factors mediating neuronal regeneration following brain injury. Understanding the factors modulating neurogenesis and neuronal regeneration in the adult nervous system has implications for the potential recovery from human brain injury and disease and the neuroprotective effects of social stimulation. [unreadable] [unreadable] [unreadable]